So I bought myself a darkglass alpha omega 900 head and I'm currently waiting for it to ship.
I did notice afterwards that it has a 4 ohm / 2 ohm switch, so I got curious, however,
I can't find what power rating the 2 ohm setting has.
8 ohm is rated at 450w (I think), 4 ohm at 900w
and 2 ohm..... I couldn't find
so what happens at 2 ohm?
Does it stay at 900w, or is it reduced or increased?
(Not well versed in this sorta stuff)
Usually this type of switch rescales the power supply to keep the current passing through the output section within a safe range. Since the model is Alpha Omega
900, it's most likely 900W at 4 and 2 ohms. However, I have seen some amps where the power at 2 ohms is less than the amp makes at 4 ohms.
For example here are the specs for the Mesa Titan: 1200 Watts @ 4 Ohms (840 Watts @ 2 Ohms, 650 Watts @ 8 Ohms),
The manual does say the 900 makes 350W at 8 ohms if you set the switch to 2 ohms.
Let's calculate the voltage at 8 ohms with the switch set to 2 ohms
We use this formulate: V=sq rt (PZ)
V=sq rt (350x8)
V=~52.92V
Now use P=(V^2)Z to see how much power we could theoretically get at 4 ohms and 2 ohms, with the switch set to 2 ohms
At 4 ohms
P=(~52.92^2)4=700W
At 2 ohms
P=(~52.92^2)2=1,400W
The amp may have other mechanisms to limit the power. For example the power supply voltage may sag under the heavy 2 ohm load, which reduces available voltage and limits power. Or the amp may use some sort of active power management (limiters and such)
Most amps with this feature require the button to be set to 2 ohms if the impedance is under 4 ohms; for example if the load is 2.67 Ohms.
If you really want to know, contact Darkglass.
I have read that these amps do have problems when run at 2 ohms with some cabs. Keep in mind that a speaker's impedance rating is nomina, and the actual impedance varies constantly as the frequency changes. At some points the impedance is under the nominal value and at other points it can be way higher than the nominal value. I think by AES standards, the impedance is only supposed to drop to 80% of the nominal value. But with some cabs the impedance drops below 80% of nominal. This sort of load can cause some amps to go into protect mode.
